Theory of light-induced effective magnetic field in Rashba ferromagnets

TL;DR

This paper theoretically investigates how short laser pulses induce effective magnetic fields in Rashba ferromagnets, highlighting the roles of optical transitions, impurity scattering, and spin-orbit interaction in the process.

Contribution

It provides a nonequilibrium formalism-based calculation of light-induced magnetic fields in Rashba ferromagnets, identifying key contributions and their dependence on system parameters.

Findings

Effective magnetic field can reach a few Tesla in Co/Pt bilayers.

The field consists of helicity-dependent and independent components with different magnetization symmetries.

The spin-orbit interaction broadens the optical transition frequency range.

Abstract

Motivated by recent experiments on all-optical magnetization reversal in conductive ferromagnetic thin films we use nonequilibrium formalism to calculate the effective magnetic field induced in a Rashba ferromagnet by a short laser pulse. The main contribution to the effect originates in the direct optical transitions between spin-split subbands. The resulting effective magnetic field is inversely proportional to the impurity scattering rate and can reach the amplitude of a few Tesla in the systems like Co/Pt bilayers. We showthat the total light-induced effective magnetic field in ferromagnetic systems is the sum of two contributions: a helicity dependent term, which is an even function of magnetization, and a helicity independent term, which is an odd function of magnetization. The primary role of the spin-orbit interaction is to widen the frequency range for direct optical transitions.